If Hex Ray deals 3 damage to a 4 might Kaisa at Dreaming Tree, then during combat the opponent plays Retreat targeting Kaisa and you respond with Stupefy to kill Kaisa, does the opponent still channel one rune and draw from Dreaming Tree?

Ruling: The opponent does not channel one rune (because Retreat's target becomes null when Kaisa dies), but they do still draw from Dreaming Tree.

Sequence:

• Hex Ray resolves, marking 3 damage on 4 might Kaisa
• Darius attacks Kaisa
• Opponent plays Retreat targeting Kaisa
• Dreaming Tree trigger is added to the chain immediately when Retreat is finalized
• You play Stupefy in response to Dreaming Tree (not Retreat)
• Stupefy resolves, reducing Kaisa to 3 might
• Cleanup occurs, killing Kaisa (3 might with 3 damage marked)
• Retreat resolves with null target, so no channel occurs
• Dreaming Tree resolves and draws a card

Nuances:

• Dreaming Tree only cares that a friendly unit was declared a target for the spell, not the outcome of the spell
• Dreaming Tree requires no additional information on resolution, so it always draws when it resolves
• Damage marked on a unit becomes lethal when the unit's might is reduced to equal the damage